Syntax
MID(sometext, beginat, howmany)
Arguments
 sometext (any textual)
 beginat (any numeric or textual) : The position, numbered from 1, of the first character in sometext to return. A real number will be rounded to the nearest integer. A textual value is equivalent to 0. beginat must be greater than 0.
 howmany (any numeric or textual) : The number of characters from sometext to return. A real number will be rounded to the nearest integer. A textual value is equivalent to 0. howmany must not be negative.
Return Value
Text: The howmany characters beginning at position beginat from sometext. If howmany is greater than the remaining length of sometext, the remainder of sometext is returned.
Examples
MID("123 Maple Dr", 5, 5)
: Maple
MID("123 Maple Dr", 5, 0)
returns blank.
Fractional Component of Decimal Value
NUMBER(MID(TEXT([Result]), (FIND(".", TEXT([Result])) + 1), LEN(TEXT([Result]))))
: Extracts the fractional component of the Decimaltype value in the Result column:

TEXT([Result])
converts the Decimal value to a Text value. The textual functions used in this example interpret nontextual values differently. Using TEXT() ensures the Result column value is interpreted the same by each function. 
FIND(".", ...) + 1
locates the beginning of the fractional component as the position immediately after the decimal point in the value. 
MID(..., ..., LEN(...))
extracts the fractional part using a howmany value guaranteed to cover the entire fractional component. 
NUMBER(...)
converts the extracted text to a Number.
See also: FIND(), LEN(), NUMBER(), TEXT()